<!doctype html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
  </head>
  <body>

    <div class="app" style="background-color:royalblue;">
      <!-- Hello -->
      <div class="test1" ></div>
      123
      <span>hello</span>
      "456"
      "789"
    </div>

    <script>
      const app = document.querySelector(".app")


      app.className = "app1 app2"

      console.log(app.outerHTML)
      app.getAttribute()
      console.log(app.attributes)
    </script>
  </body>
</html>
